Web content is most commonly found by a user-specified query. The user enters a query, in the form of a search string, into a search engine such as Google, Ask, etc., and a list of content items is returned. Certain search engines are focused on certain types of content. For example, the main search pages of Google and Ask focus on finding web pages, although most general-purpose search engines, including Google and Ask, have specialized search pages that focus on finding news, images, videos or movies, local information, etc.
Content that can be found by this method traditionally takes forms such as HyperText Markup Language (HTML), Portable Document Format (PDF), and others, although newer formats such as RSS (which, at various times, has stood for “Really Simple Syndication,” “Rich Site Summary,” and other phrases) have become popular in recent times. RSS is often used to deliver content that changes frequently. News site and weblogs (“blogs”) are examples of content that changes frequently, and for which RSS is well-suited. Many web sites that are devoted to changing content, such as those of the major news services (e.g., the New York Times, CNN, etc.), or news services with a special focus (e.g., Valleywag, TechCrunch, etc.), provide RSS feeds on their sites. These RSS feeds may provide content that is updated recurrently to reflect recent events. The web sites of bloggers, such as those who cover politics, also may post RSS feeds on their site that are recurrently updated with new content.
When a user browses the web, a record of the user's browsing is created in the form of a search history. Browsers, such as Microsoft IE and Firefox, maintain a history of sites that the user has visited. The browsing history typically records web sites that have been visited for some number of weeks in the past (e.g., the last three weeks of browsing). This record may reflect the user's browsing behavior, tastes, interests, preferences, etc. (as well as some web sites that have been visited accidentally).
Various applications may attempt to discover a user's interests, tastes, etc., for various purposes. For example, web advertisement generators may use technologies such as cookies to track user behavior and to target ads to the user based on assumptions about this behavior. Advertisement generators also direct targeted advertising to a user based on the web site that is currently being visited—e.g., if a user visits a weather web site in the winter, the advertising service may generate an advertisement for coats on the web page. Certain search engines scan e-mail for keywords, and direct advertising to the user based on the user's interest as indicated by the content of their e-mail conversations.
However, the foregoing services generally do not use the user's browsing history to select content that is appropriate for the user. Nor do these web sites use the browse history, or other mechanism, to identify categories of recurrently-changing content that may interest the user.